Sand casting is one of the methods most commonly used in foundry work, and has been developed over the years so that numerous widely differing ways now exist of obtaining molds for casting highly complex parts of good dimensional accuracy. One of the most advanced methods in this respect is what is known as “Lost Foam Casting”.
The common denominator of all sand casting methods is the use of sand as a moldable material to support the metal, and which forms a “negative” of the required casting. In the case of complex molds in particular, however, it is difficult to ensure all the gaps in the pattern (eventually forming the underside recesses or cavities in the finished part) are filled with sand to an adequate degree of compactness. Moreover, in Lost Foam Casting, there are no polymer binders added to the sand, so that the mold depends mainly on the compactness of the sand itself.
To ensure all the hollows are filled completely with sand, mechanical vibration is applied to the pattern and the formwork containing the sand, so that the sand flows into all the cavities and gaps; and complete filling of the formwork must be accompanied by adequate compacting of the sand, the absence of either one of which conditions may impair the quality, and result in rejection, of the finished casting.
At present, the only way of evaluating the compactness of the sand inside the formwork is by characterizing and controlling vibration of the formwork. Such a method, however, being indirect, still does not ensure against individual casting defects caused by inadequate local compactness or filling; which uncertainty, particularly in the case of fairly complex molds, may result in a large number of rejects.
U.S. Pat. No. 5,996,681 describes a casting mold quality control system, in which the molds are measured using proximity sensors to prevent casting defects, but which makes no provision for sand compactness evaluation.